In the wire-cut electroerosion process which is also called wire-cut or traveling-wire EDM (electrical discharge machining), a continuous electrode wire (the term is commonly used to refer to an electrically conductive wire, filament, tape, ribbon or like continuous elongate electrode element) is stored on a supply reel disposed in air and is arranged to extend continuously from this reel to takeup means over a cutting zone defined between a pair of wire guide members and supplied with a liquid machining medium such as distilled water. A workpiece is disposed in the cutting zone into and through which the electrode wire penetrates and travels in spaced juxtaposition with the workpiece. A drive means is provided downstream of one of the guide members which is disposed on the wire takeup side to unwind the electrode wire from the storage reel and to advance it along the path of wire travel so that the wire travels through and in juxtaposition with the workpiece between the guides members. An EDM power supply is connected electrically with the electrode wire and the workpiece to effect a succession of electrical discharges between the traveling wire and the workpiece, thereby electroerosively removing material from the workpiece. Wire braking means is provided on the wire supply side in the path of wire travel to apply to the advancing electrode wire a tension which must be sufficient to ensure the linearity of the electrode wire traveling through the workpiece between the wire guide members.
One of the problems which have hitherto been encountered in the wire-cut electroerosion process is breakage of the electrode wire. The traveling electrode wire tends to break when excessive heat and/or mechanical stress develops in the cutting zone.
I have discovered that these causes of breakage of the electrode wire are attributable at least partly to air bubbling in the cutting zone from the electrode wire which, after travel through the air space on the upstream side of the cutting zone, passes into and through the liquid machining medium in the latter where electrical discharges are effected generating heat to produce an elevated temperature. I have now found that the air is entrained with the traveling electrode into the liquid machining medium where it causes bubbles and the generated air bubbles tend to concentrate at a localized site in the cutting zone to create a thermal arc discharge when the electrode wire supplied from the storage reel has residual contaminants on the surface thereof. These air bubbles give rise to an extremely high mechanical stress and the resulting arc discharge constitutes a thermal source sufficient to cause the breakage of the electrode wire.